1. Field of the invention
The present invention relates to light guide plates (LGPs) of liquid crystal displays (LCDs), and backlight systems using such LGPs.
2. Description of the Prior Art
A typical LCD device comprises an LCD panel, and a backlight system mounted under the LCD panel for supplying light beams thereto. The backlight system mainly comprises a light source and an LGP. The LGP is normally a transparent polymer plate, and is used for guiding light beams emitted by the light source to uniformly illuminate the LCD panel.
FIG. 4 shows a backlight system 1 as disclosed in U.S. Pat. No. 6,443,583. The backlight system 1 includes a light source 110, a light source cover 120 and an LGP 200. The LGP 200 comprises a light incident surface 201, a light emitting surface 203 adjoining the light incident surface 201, and a bottom surface 202 opposite to the light emitting surface 203. The backlight system 1 further comprises a reflective sheet 210 underlying the bottom surface 202, a diffusion sheet 220 adjacent the light emitting surface 203, a prism sheet 230 disposed on the diffusion sheet 220, and a protecting film 240 disposed on the prism sheet 230. The prism sheet 230 serves to redirect diffused light emitting from the diffusion sheet 220 so that it is more concentrated.
In operation, the light source 110 emits light beams and the light beams are transmitted into the LGP 200. The reflective sheet 210 reflects the light beams and directs the light beams to exit from the light emitting surface 203. The light beams then sequentially pass through the diffusion sheet 220, the prism sheet 230 and the protecting film 240 to illuminate a liquid crystal panel.
However, the prism sheet 230 and the LGP 200 are conventionally fabricated as separate parts. This makes a structure of the backlight system 1 unduly complicated, and makes assembly of the prism sheet 230 and the LGP 200 unduly inconvenient.
FIG. 5 shows another kind of backlight system, as disclosed in China Patent No. 00246505. The backlight system 10 comprises an LGP 12 having a bottom surface 15 with a plurality of protrusions 17 thereon, a light emitting surface 18 with a plurality of V-shaped grooves 16 defined thereat, a diffusion film 13, a plasma film 14, and a reflective film 11. In assembly, the diffusion film 13 is attached on the light emitting surface 18 at the V-shaped grooves 16, and then the plasma film 14 is attached on the diffusion film 13. The V-shaped grooves 16 function as an equivalent of the prism sheet 230 of the backlight system 1 of FIG. 4. That is, the backlight system 10 omits any prism sheet 230. This simplifies the structure of the backlight system 10, makes assembly more convenient, and reduces costs.
In operation, the V-shaped grooves 16 serve to redirect diffused light from the protrusions 17 so that the light is more concentrated when it illuminates a panel area (not shown). However, the V-shaped grooves 16 also serve to redirect parallel light from the protrusions 17 so that the light is more concentrated when it illuminates the panel area. This results in uneven illumination, and in more severe cases dark areas appearing on the LCD panel. In order to assure that all light from the protrusions 17 is uniformly emitted at the V-shaped grooves 16, vertex angles of ridges that separate the V-shaped grooves 16 and a pitch between adjacent V-shaped grooves 16 must both be precisely calculated. This is difficult and complicated to put into practice.
It is desired to provide a backlight system and an LGP used therein which overcome the above-mentioned problems.